Scanning Accuracy and Precision in Seven Dental Scanners
Jonathan E. Fryml, Zachary W. Schurch, Walter Renne, DMD, Ray Kessler, DMD, Mark Ludlow, DMD, Abigail Lauer
The Medical University of South Carolina, College of Dental Medicine
Choosing which intraoral scanner to purchase for a dental practice can be a daunting task in light of the many brands and models that have flooded the market in recent years. This study compares the scanning accuracy of six of the most popular intraoral digital scanners as well as one model scanner. The following scanners were evaluated: 3shape Trios 3, CEREC Omnicam, CEREC Blue Cam, Planscan, Itero, Carestream 3500, and the 3Shape D800. A model was fabricated using Telio CAD A2, a product that highly resembles the optical properties of enamel. Both full arch and sextant scans were generated using each scanner. A master scan was made using an extremely high resolution scanner operated by Capture 3D. Each scan was compared to the master scan using Geomagic Control and the degree of variability was recorded.
Over the past few decades, intraoral scanners have become more common in almost every area of dentistry. Since the development of the first chairside system by CEREC in the 1980s, the technology of these machines has continued to improve. From the fabrication of crowns to night guards, the uses of computer aided design and computer aided manufacturing (CAD/CAM) have transformed the way practitioners and laboratories alike fabricate fixed and removable appliances. Because of the constantly evolving technology that each scanner employs, a comparison of accuracy is necessary to determine which scanner is the truest for both limited arch and full arch oral rehabilitation. Comparing a three dimensional analysis of a master scan by an extraoral scanner to trial scans from intraoral scanners has been the method of choice in evaluating the accuracy of these computer-aided impressions in recent studies. The main objective of this study is to determine which of the 7 scanners has the greatest accuracy in a full-arch and sextant scan through a three dimensional analysis. The null hypothesis of this study is that none of the scanners evaluated will demonstrate significant differences from the master scan.
Materials and Methods
A reference model was made using a Nissin dental typodont model of a maxillary arch that holds 14 plastic teeth. The teeth were prepared for all ceramic crowns and scanned into a CEREC Omnicam unit and 14 crowns were designed and milled out of Telio CAD A2. This material was chosen because its optical properties are more similar to tooth structure than most restorative material. The crowns were cemented onto the teeth and the teeth were fixed into place in the model so there would be no movement throughout data collection.
A master reference scan of the model was obtained from Capture 3D in Huntersville, North Carolina. The reference model was created with an ATOS Triple Scan, an industrial structured blue light 3D scanner. According to the manufacturer, this scanner is accurate to 10 microns and demonstrates repeatability of 5 microns.
Next, ten scans were performed with six different dental intraoral scanners: CEREC Omnicam, Cerec Bluecam, E4D Planmeca Planscan, Cadent iTero, Carestream 3500, and 3Shape Trios 3. One model scanner was tested- the 3Shape D800. Five full-arch scans and five sextant scans were obtained from each of the scanners. An experienced dentist and expert on each system participated in each of the scans.
Each data set was converted to an STL file. The STL files were then compared with the master STL file using a 3D analysis software program, Geomagic ControlTM. This software was formerly known as Geomagic Qualify™ 2012.
Average maximum and minimum deviation values were recorded as well as standard deviation for each scan. This data was statistically analyzed by the SPARQ research center.
Sextant Trueness (Accuracy)
Trueness represents how close the digital scan is to the actual, which is represented by the master scan. The interaction effect between location and scanner i for accuracy was found to be significant (p= 0.0090), as well as location (p=0.0465) and scanner (p<0.0001). That is, there were significant differences in type of scanner between the lower and upper locations. The results indicate that order of accuracy when scanning quadrants are from most accurate to least are Planscan>3Shape D800> CEREC Omnicam> itero> CEREC Bluecam> 3Shape TRIOS 3> Carestream 3500.
Full Arch Trueness (Accuracy)
The interaction effect in the linear mixed effects model analysis for accuracy was not found to be significant (p < 0.8). That is, the differences in the types of scanner were similar in the lower and upper locations. Therefore, the analysis was repeated without the interaction, to compare the scanner types (adjusting for the location). The scanner types were found to be significantly different (p< 0.0001). The results indicate that order of accuracy when scanning full arches are from most accurate to least are: 3Shape D800> itero> 3Shape TRIOS 3>Carestream 3500>Planscan>CEREC Omnicam>CEREC Bluecam.
The scanner found to be the most accurate for scanning sextants was the Planscan. It is an open scanner that allows free STL model export and also allows model import. The CEREC Omnicam was also found to be very accurate in sextants and was noted for being one of the fastest and easiest to use scanners. As opposed to the other systems, the CEREC remains closed in that open STL files are not natively available without additional fees. It is worth noting that CEREC Omnicam has special orthodontic software for full arch impressions that may increase the full arch accuracy with the compromise of slowing scan time. Likewise Planmeca Planscan is working on a special full arch mode, which will increase scan accuracy at the expense of slowing scan time.
It is no surprise that the 3Shape D800 laboratory scanner box has the best accuracy for full arch scanning as it was built from the ground up to accommodate full arches for laboratory use. The two intraoral scanners that performed the best for full arch were the Carestream 3500 and the Itero. The scan time was not specifically analyzed in this study however, it may be worth mentioning here that both the Carestream 3500 and iTero were the slowest systems with scan times for full arch at over 10 minutes per arch. This is due to the single image point and click scanning technology. The iTero scanner was extremely accurate in both full arch and sextant scanning. The system that had the best combination of speed and accuracy for full arch scanning was the 3shape TRIOS 3. This system was the most accurate of the video speed systems when dealing with full arch scanning and was also noted as being the fastest. Both the Planscan and the Omnicam performed well in full arch scanning but it worth noting they both lacked consistency (precision) especially the Planscan. Also the Planscan was more technique sensitive requiring a specific scan pattern where the Omnicam allowed a less technique sensitive full arch scan.
Statistical differences were observed when analyzing both the full arch and sextant scans of each of the systems evaluated; however, it is also difficult to compare this study with other studies on the topic because of the different variables, including model material, size of the arch, analysis software, operator skill, specific camera calibration etc. Furthermore, the clinical scenario was not replicated, to include temperature, soft tissue interference, humidity, saliva and patient movement. Further research needs to be conducted and a standardized method needs to be developed to evaluate and compare multiple systems.
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